Here are run-time target specifications.
This function-like macro expands to a block of code that defines
built-in preprocessor macros and assertions for the target CPU, using
builtin_assert. When the front end
calls this macro it provides a trailing semicolon, and since it has
finished command line option processing your code can use those
builtin_assert takes a string in the form you pass to the
command-line option -A, such as
cpu=mips, and creates
builtin_define takes a string in the form
accepted by option -D and unconditionally defines the macro.
builtin_define_std takes a string representing the name of an
object-like macro. If it doesn’t lie in the user’s namespace,
builtin_define_std defines it unconditionally. Otherwise, it
defines a version with two leading underscores, and another version
with two leading and trailing underscores, and defines the original
only if an ISO standard was not requested on the command line. For
__mips__ and possibly
_mips, and passing
You can also test for the C dialect being compiled. The variable
c_language is set to one of
clk_objective_c. Note that if we are preprocessing
assembler, this variable will be
clk_c but the function-like
preprocessing_asm_p() will return true, so you might want
to check for that first. If you need to check for strict ANSI, the
flag_iso can be used. The function-like macro
preprocessing_trad_p() can be used to check for traditional
TARGET_CPU_CPP_BUILTINS but this macro is optional
and is used for the target operating system instead.
TARGET_CPU_CPP_BUILTINS but this macro is optional
and is used for the target object format. elfos.h uses this
macro to define
__ELF__, so you probably do not need to define
This variable is declared in options.h, which is included before any target-specific headers.
This variable specifies the initial value of
Its default setting is 0.
This hook is called whenever the user specifies one of the target-specific options described by the .opt definition files (see Options). It has the opportunity to do some option-specific processing and should return true if the option is valid. The default definition does nothing but return true.
decoded specifies the option and its arguments. opts and
opts_set are the
gcc_options structures to be used for
storing option state, and loc is the location at which the
option was passed (
UNKNOWN_LOCATION except for options passed
This target hook is called whenever the user specifies one of the
target-specific C language family options described by the .opt
definition files(see Options). It has the opportunity to do some
option-specific processing and should return true if the option is
valid. The arguments are like for
default definition does nothing but return false.
In general, you should use
TARGET_HANDLE_OPTION to handle
options. However, if processing an option requires routines that are
only available in the C (and related language) front ends, then you
Targets may provide a string object type that can be used within
and between C, C++ and their respective Objective-C dialects.
A string object might, for example, embed encoding and length information.
These objects are considered opaque to the compiler and handled as references.
An ideal implementation makes the composition of the string object
match that of the Objective-C
NXString for GNUStep),
allowing efficient interworking between C-only and Objective-C code.
If a target implements string objects then this hook should return a
reference to such an object constructed from the normal ‘C’ string
representation provided in string.
At present, the hook is used by Objective-C only, to obtain a
common-format string object when the target provides one.
Declare that Objective C class classname is referenced by the current TU.
Declare that Objective C class classname is defined by the current TU.
If a target implements string objects then this hook should return
true if stringref is a valid reference to such an object.
If a target implements string objects then this hook should provide a facility to check the function arguments in args_list against the format specifiers in format_arg where the type of format_arg is one recognized as a valid string reference type.
This target function is similar to the hook
but is called when the optimize level is changed via an attribute or
pragma or when it is reset at the end of the code affected by the
attribute or pragma. It is not called at the beginning of compilation
TARGET_OPTION_OVERRIDE is called so if you want to perform these
actions then, you should have
This is similar to the
but is only used in the C
language frontends (C, Objective-C, C++, Objective-C++) and so can be
used to alter option flag variables which only exist in those
Some machines may desire to change what optimizations are performed for various optimization levels. This variable, if defined, describes options to enable at particular sets of optimization levels. These options are processed once just after the optimization level is determined and before the remainder of the command options have been parsed, so may be overridden by other options passed explicitly.
This processing is run once at program startup and when the optimization
options are changed via
#pragma GCC optimize or by using the
Set target-dependent initial values of fields in opts.
Some targets like RISC-V might have complicated multilib reuse rules which are hard to implement with the current multilib scheme. This hook allows targets to override the result from the built-in multilib mechanism. switches is the raw option list with n_switches items; multilib_dir is the multi-lib result which is computed by the built-in multi-lib mechanism; multilib_defaults is the default options list for multi-lib; multilib_select is the string containing the list of supported multi-libs, and the option checking list. multilib_matches, multilib_exclusions, and multilib_reuse are corresponding to MULTILIB_MATCHES, MULTILIB_EXCLUSIONS, and MULTILIB_REUSE. The default definition does nothing but return multilib_dir directly.
Some targets need to switch between substantially different subtargets
during compilation. For example, the MIPS target has one subtarget for
the traditional MIPS architecture and another for MIPS16. Source code
can switch between these two subarchitectures using the
Such subtargets can differ in things like the set of available registers, the set of available instructions, the costs of various operations, and so on. GCC caches a lot of this type of information in global variables, and recomputing them for each subtarget takes a significant amount of time. The compiler therefore provides a facility for maintaining several versions of the global variables and quickly switching between them; see target-globals.h for details.
Define this macro to 1 if your target needs this facility. The default is 0.
Returns true if the target supports IEEE 754 floating-point exceptions
and rounding modes, false otherwise. This is intended to relate to the
double types, but not necessarily
By default, returns true if the
adddf3 instruction pattern is
available and false otherwise, on the assumption that hardware floating
point supports exceptions and rounding modes but software floating point